In drilling an oil well, especially at an offshore location, it is necessary to install flanges of various sizes of large diameter pipe. Consider, as an example, the instance where several sizes of casing are installed in a well. The well might include, as an example, a 36 inch drive pipe. There may also be a 20 inch casing, 133/8ths inch casing and 95/8ths inch casing. It is necessary to install a termination flange or casing head at every change of size. The flange is typically installed by first cutting the casing, preheating the casing and then welding the flange in place. The flange is necessary to mount other equipment or to otherwise isntall the next casing string.
Often, this requires cutting a very thick wall casing, even in the range of 11/2 inch thick and thereafter making a multi-pass welded bead to attach the flange. This requires a tremendous amount of preheating to obtain a quality weld.
For drilling rigs located at sea, the preheating is something of a problem. In inclement weather, wind shields must be installed and a number of welders will position their torches on the casing and flange to preheat it for perhaps 4 to 6 inches below the casing head in length to perhaps 500.degree. F. This is difficult and time consuming. Moreover, cooling begins on the instant that preheating is stopped. It is difficult to preheat the casing and simultaneously weld a flange to it.
Certain devices have been provided heretofore to serve as preheaters. While these devices have various and sundry advantages, it is believed that the device of this disclosure is much more attractive for the intended purpose, namely to provide a preheater which can be selectively installed within a casing, whereby preheating occurs from the interior. This enables the welder to install the flnage or casing head and quickly begin the multi-pass bead required to fasten the flange in place.
The various preheater devices are typified by the patent of Jaeger, U.S. Pat. No. 3,082,760. However, this device and others like it are believed to be limited. There is a real risk that the preheater device will be lost down the casing. If this occurs, it may then be lost in the wellbore. In the wellbore, it poses a serious problem. It is necessary to remove it because it is very difficult to drill through the steel Jaeger device. In either case it is not very desirable.
The preheater device of this disclosure utilizes a cement receptable which is non-corrosive to saltwater, relatively inexpensive, and able to be broken into small pieces should it fall into the wellbore. It is relatively easy to drill through the cement device. This does not impede the drilling process that occurs subsequently to the use of the preheater device.
The present disclosure is therefore directed to a preheater device which is formed of a cement body of frangible material. This includes a bottom cylindrical receptacle. It terminates at the center in an upstanding stalk with light weight chain pre-cast through the length of the body. The cement body is self-centralizing and supports an elongate cast cylindrical exothermic compound. One suitable material is molded thermite. A deflector plate made of the same cement is positioned on the top. It is sized relative to the casing to direct the flow of hot gases outwardly and against the wall of the casing to be heated. The device is held in place by a chain attached to one of the utility hoist cables common to all drilling rigs.